1. Field of the Invention
This invention relates to internal combustion engines, and is directed more particularly to a method for converting a four-stroke cycle diesel engine to a spark ignition natural gas fueled engine.
2. Description of the Prior Art
The conversion of diesel engines to natural gas engines is generally known. Such conversions have involved replacing the diesel fuel injectors with spark plugs connected to a suitable ignition system, and providing a carburetor on the intake manifold. In U.S. Pat. No. Re. 26,145, reissued Jan. 24, 1967, to James F. Friddell, such conversions are discussed, along with an improvement for no-load or low-load applications.
In U.S. Pat. No. 4,911,124, issued Mar. 27, 1990, to John R. M. Bennett, there is described rocker and fulcrum mechanism by which the opening of the exhaust valves of the engine is reduced to minimize reflux of exhaust gases into the combustion chamber.
U.S. Pat. No. 5,000,138, issued Mar. 19, 1991, to John R. M. Bennett, is directed to a method for installing spark plugs in a diesel internal combustion engine for converting the engine for use with gaseous fuel.
Such prior art conversions typically require modification of the piston or cylinder head to reduce the compression ratio to a value suitable for natural gas. The effort and expense required to develop a new piston and/or cylinder head can be substantial and, once done, will not be generally applicable to a variety of engines.
Further, in turbo-charged diesel engines, wherein air is forced under pressure into an intake manifold and thence into the cylinder, the valve timing is such that scavenging occurs at the end of the exhaust stroke and the beginning of the intake stroke. If left unremedied in conversion to gas, such timing leads to loss of fuel directly to the exhaust, affecting the thermal efficiency of the engine and emissions.
It therefore would be beneficial to have available a method by which a diesel engine could be converted to run on natural gas, without the requirement of substantial modification or replacement of the cylinder heads and/or pistons, and which would provide for proper timing of exhaust valve and inlet valve operation.